This investigation should contribute to an improved understanding of periodontal disease by providing immunochemical information about cell surface antigens which may act as virulence factors for Actinomyces viscosus T14V. This organism is associated with plaque, root surface caries and the immunological sensitization of periodontal disease patients, and it also causes periodontal lesions in gnotobiotic rats. A mutant strain (T14AV) is avirulent for rodents and lacks an antigen (V-antigen) which is present in the virulent strain. The V-antigen is being purified from cell wall extracts. It will be characterized by its: approximate molecular weight, sugar and amino acid composition, immunodominant groups, and its effects on lymphocytes and osteoclasts. Homogeneous proteins (lectins and mouse myeloma proteins) will be screened to detect binding activities for the V-antigen and other cell surface antigens from A. viscosus.